1. Field of the Invention
The present invention relates to a device which combines the functions of a directional gyro (DG) and navigation radio indicator in a single instrument for aircraft.
2. Description of the Related Art
The conventional method of presenting heading and course information on an aircraft panel is by using two instruments; a directional gyro (DG) for heading, and a navigation radio indicator for course. The DG has a rotating dial (360.degree.) display with the present heading appearing at the top of the instrument as the airplane moves in azimuth. The navigation radio indicator has an omni bearing selector (OBS) dial (360.degree.) which can be rotated manually to select a particular navigation radio course. It has a course deviation indicator that moves in relation to the aircraft's position with respect to the selected navigation radio course, and a To-From indicator to eliminate reciprocal ambiguity. These two instruments are simple and reliable, and they provide all of the heading and course information necessary for normal aircraft navigation. This two instrument display was used by practically all aircraft for many years and is still used today by most small single engine aircraft. Also included in some navigation radio indicators is a glide slope indicator which moves in relation to the aircraft's position relative to the glide slope beam of an instrument landing system (ILS).
Although the two instrument system described above provides all necessary heading and course information, interpreting the relationship between heading and course can be a complex mental integration exercise. In order to simplify this integration problem, the horizontal situation indicator (HSI) was developed. This is a single instrument that combines the DG and navigation radio indicator functions in one display. This was an excellent solution to the problem, and HSI's are found on most large aircraft today. The HSI is very expensive, however, and is financially out of reach for most small single engine aircraft owners. Some years ago, the directional gyro-omni (DGO) was developed which was a low cost version of the HSI. The DGO (U.S. Pat. No. 3,806,865) was not commercially successful because of poor reliability caused by extreme mechanical complexity and the undesirable feature that a new course could not be selected unless the aircraft was in straight and level flight. It was taken out of production after about five years. At present, there are no combined display instruments available at a cost that allows usage on small single engine aircraft.
The problems or disadvantages which the piror DGO had which finally led to its commercial demise were:
1. It was necessary to cage the gyro in order to select a new course, meaning a new course could only be selected in straight and level flight.
2. It had an eight circuit brush block/slip ring assembly with very low level current passing through it that was subject to intermittent operation because of easy susceptibility to contamination by minute particles.
3. It used a potentiometer for the electrical portion of the OBS function which was also easily susceptible to contamination by minute particles.
4. It used a clutch-brake mechanism for the mechanical portion of the OBS function which was complex and unreliable.
5. It had two meters mounted on a freely rotating dial assembly that were susceptible to "bouncing on the stop" under normal aircraft vibration.
The present invention has as its advantages the elimination of the problems of the prior DGO device while retaining the functions and low cost thereof. The fact that the heading card is driven directly by the DG allows the cost to be maintained within the means of most small aircraft owners. A particular feature of the present invention is a cross pointer display of the course deviation indicator and the glide slope indicator in front of a compass card with course select pointer. Another particular feature of the present invention is the manner in which the selected course can be changed without the need for caging the gyro. An additional feature is the manner in which the selected course information is generated and transmitted to the navigation radio.
These particular features result in an integrated navigation display at a relatively low cost, free of the severe problems associated with the previous DGO.